CONFIG_DEBUG_KMEMLEAK_VERBOSE sends every report to the console, so a transient false positive there is broadcast to whatever collects the kernel log rather than sitting in the debugfs file until someone looks. That asymmetry justifies being more conservative than the general case.
Require one more consecutive unreferenced scan before reporting. The only cost is that a genuine leak is reported one scan interval later (600s by default); the value stays writable at run time through the module parameter. Kernels without CONFIG_DEBUG_KMEMLEAK_VERBOSE keep reporting on the first unreferenced scan. I've been running constant upstream kernel with CONFIG_DEBUG_KMEMLEAK_VERBOSE set, and I am still seeing some rare false positive, that goes away with min_unref_scans=3, so, making it the default based on my heuristic. Signed-off-by: Breno Leitao <[email protected]> --- Documentation/dev-tools/kmemleak.rst | 2 +- mm/kmemleak.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/Documentation/dev-tools/kmemleak.rst b/Documentation/dev-tools/kmemleak.rst index b5fe7e671d0f8..c0d3293723425 100644 --- a/Documentation/dev-tools/kmemleak.rst +++ b/Documentation/dev-tools/kmemleak.rst @@ -206,7 +206,7 @@ the minimum age of an object to be reported as a memory leak. The ``min_unref_scans`` module parameter requires an object to be seen unreferenced in that many consecutive scans before it is reported. It -defaults to 2 when CONFIG_DEBUG_KMEMLEAK_VERBOSE is enabled, where the +defaults to 3 when CONFIG_DEBUG_KMEMLEAK_VERBOSE is enabled, where the periodic scan thread confirms a leak on its own, and to 1 otherwise. A value of 1 preserves the historical behaviour; higher values filter the transient false positives described above, at the cost of delaying genuine diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 8fa409a4f9fb2..5d0daea93c471 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -238,7 +238,7 @@ static struct task_struct *scan_thread; static unsigned long jiffies_min_age; /* consecutive scans an object must stay unreferenced before reporting */ static unsigned int min_unref_scans = - IS_ENABLED(CONFIG_DEBUG_KMEMLEAK_VERBOSE) ? 2 : 1; + IS_ENABLED(CONFIG_DEBUG_KMEMLEAK_VERBOSE) ? 3 : 1; module_param(min_unref_scans, uint, 0644); static unsigned long jiffies_last_scan; /* delay between automatic memory scannings */ -- 2.53.0-Meta
